A wireless communications network typically includes a variety of communication nodes coupled by wireless or wired connections and accessed through different types of communications channels. Each of the communication nodes includes a protocol stack that processes the data transmitted and received over the communications channels. Depending on the type of communications system, the operation and configuration of the various communication nodes can differ and are often referred to by different names. Such communications systems include, for example, a Code Division Multiple Access 2000 (CDMA2000) system and a Universal Mobile Telecommunications System (UMTS).
Third generation wireless communication protocol standards (e.g., 3GPP-UMTS, 3GPP2-CDMA2000, etc.) may employ a dedicated traffic channel in the uplink (e.g., a communication flow between a mobile station (MS) or User Equipment (UE), and a base station (BS) or NodeB. The dedicated physical channel may include a data part (e.g., a dedicated physical data channel (DPDCH) in accordance with UMTS Release 4/5 protocols, a fundamental channel or supplemental channel in accordance with CDMA2000 protocols, etc.) and a control part (e.g., a dedicated physical control channel (DPCCH) in accordance with UMTS Release 4/5 protocols, a pilot/power control sub-channel in accordance with CDMA2000 protocols, etc.).
Newer versions of these standards, for example, Release 6 of UMTS provide for high data rate uplink channels referred to as enhanced dedicated physical channels. These enhanced dedicated physical channels may include an enhanced data part (e.g., an enhanced dedicated physical data channel [E-DPDCH] in accordance with UMTS protocols) and an enhanced control part (e.g., an enhanced dedicated physical control channel [E-DPCCH] in accordance with UMTS protocols). As defined in the specification of the enhanced uplink data channel, the UE transmits a frame of data in the E-DPDCH simultaneously with a frame of control information in the E-DPCCH channel. This control information communicated from UE to NodeB includes parameters that are in general necessary for NodeB to decode the E-DPDCH frame. An E-DPCCH word includes seven E-TFCI (E-DCH [enhanced-uplink dedicated channel] transport format combination indicator) bits that provide to the NodeB information from which NodeB can determine actual combination of predefined transport channels within the E-DPDCH data frame, including the packet size for each individual transport channel. This is needed because multiple transport channels can be multiplexed into the physical channel based on the type of the applications and the dynamic nature of packet data communication. Generally, two frame sizes (TTI lengths), i.e., 10 ms and 2 ms, are available for use in the E-DPDCH. In addition, an E-DPDCH word includes two RSN (retransmission sequence number) bits that indicate the redundancy version of the data frame. The redundancy version is needed because the NodeB needs to know whether a frame is transmitted for the first time, or a HARQ (Hybrid Automatic Repeat Request) retransmission of theframe, and specifically whether it's a second, third or larger than third transmission of the dataframe. If a previous transmission has not been acknowledged by any of the NodeBs that might be communicating with a UE, the UE will retransmit the same frame unless an acknowledgement (ACK) is received from at least one NodeB, or the maximum allowable number of retransmissions of the same frame has been reached. Therefore, even if a NodeB was not able to decode a frame transmission previously, it cannot predict whether the UE will send a new transmission of another frame or the retransmission of the previous frame since the previous frame might have been acknowledged by another NodeB with which the UE was communicating. The E-DPCCH word also includes a single happy bit (H-bit), which indicates to the NodeB that the UE wants to transmit at a higher or lower rate. An E-DPCCH word contains 10-bits.
The E-DPCCH is usually transmitted with sufficient power to guarantee that the NodeBs can decode this channel correctly. For UEs that transmit E-DPDCH with a large number of data bits per frame, the total power given to the E-DPCCH channel is only a small fraction of the power given to all E-DPDCH channels. However, for applications such a VolP (Voice-over-IP), the UEs transmits E-DPDCH with a small number of data bits per frame only. In this latter case, the power given to E-DPCCH is significant compared with the power given to the corresponding E-DPDCH of the same UE. There are also other situations where E-DPCCH power is significant compared to the E-DPDCH power, which is the case whenever UEs are transmitting with low data rates on E-DPDCH. In particular, very low data rates are often assigned to UEs with unfavorable path loss conditions in heavily loaded cells.
Disadvantageously, the additional power required for transmitting E-DPCCH can significantly reduce the overall capacity on the reverse channel. As noted, there are two different frame sizes (10 ms and 2 ms TTI lengths). For VolP applications, the 2 ms TTI length may be preferred since it introduces less delay as compared with the 10 ms TTI length, in particular when using a larger number of HARQ retransmissions leading to improved time diversity. The overhead due to E-DPCCH is even more significant for a 2 ms TTI length, however, because there is a higher effective E-DPCCH data rate and less diversity gain as compared to the case of a 10 ms TTI length.